The following is a brief description of the physiological role of NF-.kappa.B. The discussion is not meant to be complete and is provided only for understanding of the invention that follows. This summary is not an admission that any of the work described below is prior art to the claimed invention.
The nuclear DNA-binding activity, NF-.kappa.B, was first identified as a factor that binds and activates the immunoglobulin .kappa. light chain enhancer in B cells. NF-.kappa.B now is known to activate transcription of a variety of other cellular genes (e.g., cytokines, adhesion proteins, oncogenes and viral proteins) in response to a variety of stimuli (e.g., phorbol esters, mitogens, cytokines and oxidative stress). In addition, molecular and biochemical characterization of NF-.kappa.B has shown that the activity is due to a homodimer or heterodimer of a family of DNA binding subunits. Each subunit bears a stretch of 300 amino acids that is homologous to the oncogene, v-rel. The activity first described as NF-.kappa.B is a heterodimer of p49 or p50 with p65. The p49 and p50 subunits of NF-.kappa.B (encoded by the nf-.kappa.B2 or nf-.kappa.B1 genes, respectively) are generated from the precursors NF-.kappa.B1 (p105) or NF-.kappa.B2 (p100). The p65 subunit of NF-.kappa.B (now termed Rel A) is encoded by the rel A locus.
The roles of each specific transcription-activating complex now are being elucidated in cells (N. D. Perkins, et al., 1992 Proc. Natl Acad. Sci U.S.A. 89, 1529-1533). For instance, the heterodimer of NF-.kappa.B1 and Rel A (p50/p65) activates transcription of the promoter for the adhesion molecule, VCAM-1, while NF-.kappa.B2/RelA heterodimers (p49/p65) actually inhibit transcription (H. B. Shu, et al., Mol. Cell. Biol. 13, 6283-6289 (1993)). Conversely, heterodimers of NF-.kappa.B2/RelA (p49/p65) act with Tat-I to activate transcription of the HIV genome, while NF-.kappa.B1/RelA (p50/p65) heterodimers have little effect (J. Liu, N. D. Perkins, R. M. Schmid, G. J. Nabel, J. Virol. 1992 66, 3883-3887). Similarly, blocking rel A gene expression with antisense oligonucleotides specifically blocks embryonic stem cell adhesion; blocking NF-.kappa.B1 gene expression with antisense oligonucleotides had no effect on cellular adhesion (Narayanan et al., 1993 Mol. Cell. Biol. 13, 3802-3810). Thus, the promiscuous role initially assigned to NF-.kappa.B in transcriptional activation (M. J. Lenardo, D. Baltimore, 1989 Cell 58, 227-229) represents the sum of the activities of the rel family of DNA-binding proteins. This conclusion is supported by recent transgenic "knock-out" mice of individual members of the rel family. Such "knock-outs" show few developmental defects, suggesting that essential transcriptional activation functions can be performed by more than one member of the rel family.
A number of specific inhibitors of NF-.kappa.B function in cells exist, including treatment with phosphorothioate antisense oliogonuoleotide, treatment with double-stranded NF-.kappa.B binding sites, and over expression of the natural inhibitor MAD-3 (an I.kappa.B family member). These agents have been used to show that NF-.kappa.B is required for induction of a number of molecules involved in inflammation, as described below.
NF-.kappa.B is required for phorbol ester-mediated induction of IL-6 (I. Kitajima, et al., Science 258, 1792-5 (1992)) and IL-8 (Kunsch and Rosen, 1993 Mol. Cell. Biol. 13, 6137-46).
NF-.kappa.B is required for induction of the adhesion molecules ICAM-1 (Eck, et al., 1993 Mol. Cell. Biol. 13, 6530-6536), VCAM-1 (Shu et al., supra), and E-selectin (Read, et al., 1994 J. Exp. Med. 179, 503-512) on endothelial cells.
NF-.kappa.B is involved in the induction of the integrin subunit, CD18, and other adhesive properties of leukocytes (Eck et al., 1993 supra).
The above studies suggest that NF-.kappa.B is integrally involved in the induction of cytokines and adhesion molecules by inflammatory mediators. Two recent papers point to another connection between NF-.kappa.B and inflammation: glucocorticoids may exert their anti-inflammatory effects by inhibiting NF-.kappa.B. The glucocorticoid receptor and p65 both act at NF-.kappa.B binding sites in the ICAM-1 promoter (van de Stolpe, et al., 1994 J. Biol. Chem. 269, 6185-6192). Glucocorticoid receptor inhibits NF-.kappa.B-mediated induction of IL-6 (Ray and Prefontaine, 1994 Proc. Natl Acad. Sci U.S.A. 91, 752-756). Conversely, overexpression of p65 inhibits glucocorticoid induction of the mouse mammary tumor virus promoter. Finally, protein cross-linking and co-immunoprecipitation experiments demonstrated direct physical interaction between p65 and the glucocorticoid receptor (Id.).